As the image sensor and optical technology progresses, hand-held devices and small sized optical applications become popular. Further, with the development of higher performance cellular phones and portable cameras, small sized image modules and lens systems with high optical quality, fast focusing speed, and low power consumption are currently under development. Especially, the advances of image sensors in the field of miniaturization and highly dense pixels increase the need of optical module or lens system with high resolution performance and more compactness. Due to the optical configuration and constraints, the size of hand-held devices has limitation to become smaller.
In response to such needs, a small number lens construction may be used in order to satisfy the requirements of compactness and low cost. Because of the constraint of small number of optical lenses, aspheric surface design becomes popularly spread in order to achieve higher performance.
Conventional automatic focusing systems perform their automatic focusing by moving one or more lenses using an electro-magnetically driven motor and/or piezo-electrically actuated apparatus. Since the lens or lenses in those systems have a considerable inertia and need to have macroscopic mechanical motions, the automatic focusing systems require a macroscopic actuator generating large actuating force. The macroscopic actuator can cause many problems including increase in size, large power consumption, slow focusing time, and eventually decrease in the probability of the imaging system. The automatic focusing can be performed by moving a sensor, as well. But, it also requires a macroscopic actuator with additional complexity necessary to satisfy electrical connection. Alternatively, a movable mirror can be used for simpler automatic focusing. The movable mirror can provide a simple and reliable automatic focusing, but it still requires a macroscopic actuator.
The compact auto-focus image taking lens system with a Micromirror Array Lens and a lens-surfaced prism of the present invention has many advantages over the prior arts in the field of invention, such as compactness in thickness, small number of optical elements, higher performance of optical quality, fast focusing speed, low power consumption, enough space for optional elements such as infrared cut-off filter and diversity in optical geometry.